The present invention claims a priority based on the patent application H8-206602 filed in Japan on Jul. 17, 1996, the content of which is incorporated hereinto by reference.
1. Field of Invention
The present invention generally relates to an autocorrelation coefficient operator for audio signal processing. In particular, the present invention relates to an autocorrelation coefficient operator, which determines an autocorrelation coefficient of an input signal at high speed with low power consumption.
2. Description of Related Art
Various kinds of autocorrelation, such as proximity correlation between sampled values and long run correlation among vowel pitch cycles, are determined in audio signal processing. For example, proximity correlation between sampled values is used for estimating spectrum characteristics of audio signals. Such a process often finds a linear estimate coefficient using an audio autocorrelation, which divides the audio signal by 20 msec (160 samples). Formula (1) shows a general operation for finding the autocorrelation coefficient R(I) of an audio signal with the number N of the sampling values and sampling delay I. ##EQU1##
As the formula (1) shows, a plurality of integration operations is necessary to find the autocorrelation coefficient. The values N and I could be different for different coding methods, and the integration operation may require an enormous number of multiplication and adding operations for large values N and I.
Conventionally, a DSP (Digital Signal Processor) conducts these operations by repeating the multiplication and adding operations. For example, to find the 10th degree autocorrelation when the sampling frequency is 8000 Hz, with a frame length of 20 msec (160 samples), the DSP must conduct 1760 operations, since 160 (integration: tap amount).times.11 (shift amount: 0th to 10th)=1760.
As shown above, audio signal processing using an autocorrelation coefficient takes a long time since enormous number of operations must be repeated. Thus, each operation has to be conducted at high speed and the DSP consumes a great amount of power, necessitating in short talking period on portable terminals, such as portable telephones, which use the integration operation for audio signal processing.